What is Asymmetrically Strengthened Glass?

The other day my friend and colleague Carl Tompkins from Sika gave me a call questioning a term found in the 2013 NAGS Catalog. On the 2013 Honda Odyssey, NAGS refers to asymmetrically strengthened glass (ASG). As soon as I learned how to spell it, (thanks spell check), I decided to look it up and see what it was.

What I found was a patent on the idea from Shandon Dee Hart, patent number US20130127202 A1. In the patent description it is described as a glass assembly of components that when put together deliver a product that has uses in many different industries. In the patent, Mr. Hart uses the automotive windshield as a practical example.

The ASG is basically an outside piece of glass that is harder than the inside piece of glass and bonded together with a laminant of unspecified material. The harder outside lite is more impact resistant, while the inside lite allows for impact absorption similar to the current windshield we know today.

The patent mentions numerous ways the outside lite can be hardened, such as films applied, thicker glass, added ingredients in the batch or processes to make the glass harder—similar to how tempered glass is hardened. At this point, I do not know what Honda has done to its glass to meet the meaning of this term but I’m hoping to do more research and let you know.

What does this mean for the future of auto glass replacement? The purpose of the harder outside layer is for impact resistance, and if it works, there will be fewer windshields to be put in. However, the jury is still out on ASG when it comes to break resistance and safety to the occupants.

ASG may be resistant to blunt force impact, but what about a sharp-edged rock travelling at 60 mph? Will the advanced glass design be resistant to that sort of force? It should be interesting to see the data after a few years of tracking the results. Will the cost increase in glass manufacture justify the use of the new types of glass design? Again, time will only tell.

Then I asked myself, does this added feature make the glass more or less safe? That remains to be seen. It could be argued that the windshield with a harder outside lite may cause more injury because the glass will not give as much as it did with a softer outside lite. One of the purposes of the lamination is to cushion the body in a collision and absorb some of the trauma of impact. If the outside lite is harder, the body will not be cushioned as much so injuries could be worse.

Whatever the results of this experiment with advanced glass design yields, we have to be prepared to replace it in the same safety conscious way as we do today. Because, let’s face it, it will break.